Cationic amphiphilic lipids constituent a vast class of vectors commonly used for the vectorisation of nucleic acids (pDNA, siRNA, mRNA) in vitro or in vivo.
Since the pioneering work of Felgner et al. (Felgner, P. L. G.; Gadek, T. R.; Holm, M.; Roman, R.; Chan, H. W.; Wenz, M.; Northrop, J. P.; Ringold, M. G.; Danielsen, M. Proc. Natl. Acad. Sci. U.S.A., 1987, 84, 7413-7417), efforts have been made to propose novel structures of cationic amphiphilic lipids that make it possible to improve the effectiveness of the transfection and to expand the knowledge of transfection mechanisms.
Transfection is carried out thanks to supramolecular aggregates formed by the association of a cationic amphiphilic lipid with DNA (lipoplexes). After the cellular internalisation of these lipoplexes which is produced by endocytosis pathway, the release of the nucleic material from the endosomes to the cytosol is necessary in order to prevent degradation of the loaded material inside the lysosomes.
Different strategies based on a molecular approach have been explored to promote the destabilisation of the endosomal membrane or act on the stability of lipoplexes after the cellular internalization thereof.
As such novel cationic amphiphilic lipids that can be protonated in the endosomes (proton sponge effect) or cleaved by an enzymatic or redox reaction in the cytosol have been proposed to destabilise the endosomal membrane.
Another strategy for improving the efficiency of transfection consists in improving the stability and the fusion properties of lipoplexes (a) Ewert, K.; Slack, N. L.; Ahmad, A.; Evans, H. M.; Lin, A. J.; Samuel, C. E.; Safinya, C. R. Curr Med Chem., 2004, 11, 133-49; b) Dan, N.; Danino, D. Adv Colloid Interface Sci., 2014, 205, 230-9). Work in particular has provided an improvement in transfections by associating co-lipids such as 1,2-dioleoyl-sn-glycero-3-phosphoetanolamine (DOPE) with a cationic amphiphilic lipid. This improvement is attributed to the propensity of DOPE to adopt a reversed hexagonal phase which is known to be more fusogenic than the lamellar phases.
Another strategy for producing non-lamellar phase consists in acting on the molecular form of cationic amphiphilic lipids. Ewert et al. reported the synthesis of cationic amphiphilic lipids having a dendretic head group (Ewert, K. K.; Evans, H. M.; Zidovska, A.; Bouxsein N. F.; Ahmad, A.; Safinya, C. R. J. Am. Chem. Soc. 2006, 128, 3998-4006). The shape of this cationic polar head induced the formation of hexagonal phases HI when they are included in a binary formulation. High transfection efficiencies were observed on cell lines known to be difficult to transfect. Lindberg et al have shown that the incorporation of two phytanyl chains (methylated C16-alkyl chains) into the cationic lipo-phosphoramidate structure produces a reversed hexagonal phase after the formulation in water (Lindberg, M.; Carmoy, N.; Le Gall, T.; Fraix, A.; Berchel, M.; Lorilleux, C.; Couthon-Gourvès, H.; Bellaud, P.; Fautrel, A.; Jaffrès, P. A.; Lehn, P.; Montier, T. Biomaterials 2012, 33, 6240-6253). Good in vivo transfection efficiencies were obtained with this vector.
Despite all this work there is still a need for developing novel vectors.
It is also desirable that these novel amphiphilic lipids be obtained by synthesis routes optimised for large-scale production required for in vivo experiments. However, there is still a need for developing a novel method of synthesis making it possible to obtain novel branched amphiphilic lipids from a simple modification of the existing amphiphilic lipid structures, allowing a high modularity and not involving a synthesis de novo, i.e. completely synthesizing the desired molecule.